I've been dating this girl Katie for 3 years, since we were both 17 at the time this happened, both or our parents were divorced and her mom was very attractive and flirty with me, even to the point where she would be partly nude in front of me when I was over. My girlfriend said that it was just her way of being a jerk. Then her mom told me stories about her and her sex life and how often she masturbates, right in front of her own daughter. Then I get a message from my girlfriend asking me to come over, when I get there I knock and her mom answers. She then tells me that Katie is at her dad's for the weekend and must have left her phone. Then tells me that she sent the message asking me to come over and tells me to follow her to the bedroom.She starts getting undressed saying that shes been really into me and that she wanted to make sure I'd be good for her daughter. She came over and jerked my pants down and starting giving me a handjob and then got onto her knees and started giving me head. I feel awful saying this but I enjoyed it so much, I started fucking her face and grabbing her breasts and I said I was coming and she pulled it out of her mouth and let me cum all over her face and breasts. She smiled and looked the other way for a second, and then she just stopped. My girlfriend was standing in the bedroom doorway, watching what just happened. I think she came back to get her phone. I felt so awful that I did that with her mom. We broke up over it and haven't talked since, but I've gone back to her mom twice more. We had sex both of those times. But now she's fucking the manager of her current workplace and said that I needed to find someone my own age and that it was wrong.